Papers by Keyword: Variability

Abstract: Leachate treatment is a critical component of municipal solid waste management due to the complex and variable nature of leachate composition. This study investigates a dilution-based strategy to address insufficient leachate volume during a mandated 21-day reliability test at the Kelaniya Transfer Station leachate treatment plant, part of the Metro Colombo Solid Waste Management Project. The primary objective was to evaluate the plant's capacity to treat leachate under continuous operational conditions at its design flow rate of 160 m³/day, despite a limited leachate supply caused by non-functional compactors. A dilution ratio of 50–60% was applied to available leachate to meet volume requirements, with the underlying assumption that such dilution would not significantly alter leachate variability. Baseline and incoming leachate samples were analyzed for key parameters, chemical oxygen demand (COD), ammonia nitrogen (NH₄–N), total nitrogen (TN), and total suspended solids (TSS). Statistical tests, including two-sample t-tests and Levene’s tests, were conducted to assess variability before and after dilution. The results revealed significant variation between undiluted samples from the same source, confirming the inherent variability of leachate. However, Levene’s tests showed no statistically significant differences in variance for NH₄–N, TN and TSS before and after dilution, indicating that the dilution process preserved the natural variability of leachate characteristics. The findings support the use of controlled dilution as a valid strategy for leachate volume supplementation during performance testing, without compromising the reliability of treatment plant assessment. Nevertheless, dilution reduces nutrient loading, particularly carbon input, and may not reflect peak loading scenarios. To address this, a supplementary a separate testing phase was conducted using undiluted leachate with high-strength characteristics over a period, specifically to evaluate the treatment plant’s capacity to handle peak loading scenarios.

Abstract: Computer simulation plays a crucial role in the designing of sheet metal stamping processes for the prediction of process output, before try-out die sets are manufactured. Different commercial software packages are available on the market for sheet forming simulation, but their accuracy can vary, depending on the selection of the pre-processing parameters and on their formulation. Software benchmarking can be used to select the most appropriate package for a given application. Calibration, i.e. the inverse determination of the correct set of pre-processing parameters, can be used for improving the prediction accuracy. The scientific literature on numerical simulations of sheet metal forming processes presents some examples of software calibration and very few examples of benchmarking. The literature generally neglects a critical and important issue: the inherent variability of real forming processes. In this work, the experimental results of two similar multi-stage deep drawing processes are presented and compared to the simulation output of two popular software packages used in the industry. Statistical methods for benchmarking and calibration are proposed. The paper demonstrates how benchmarking can be misleading if process variability is not considered.

Abstract: Earthen materials have different nature components and present a high variability comparing to conventional materials; researchers try to settle it down for a future normalization as environmentally efficient material. But there is a need in energy to do it, either directly (compaction, organic matter extraction, particle screening to get the best particle size distribution ...) or indirectly by including inefficient materials from an environmental perspective (cement, limestone ...). The aim of this study is to follow the variability problematic of cob materials by comparing and understanding variation level of the hygrothermal characteristics due to fibres nature and fibres content. We found that plant fibres (hemp, flax and hay) act as a stabilizer for dry bulk density; at 1% fibres substitute, hemp fibre composites show the highest coefficient of variation on the thermal properties (6.1% on thermal conductivity, 18.74% on specific heat capacity) but flax fibres show the highest mean values. Increasing hay stalk content induces the spread of the hygrothermal properties inside their range of variaation.

Abstract: Locally available and with infinite recycling possibilities, the use of earth as building material leads to one of the lowest environmental impacts in the construction sector. Recent advances in the earth materials field have been made based on concrete and ceramics technologies to facilitate its uses in dense areas. It is possible to modify clay particle interactions and the material's whole behavior by adding inorganic dispersants and flocculants into clay paste. Earth becomes easy to cast and unmold into formworks, and by removing cement in its composition, poured earth can reach a low CO₂ emission rate. Even if this technology is promising, further work has to be performed, as it cannot be implemented on earth from excavation sites with high variability. Tackling the clay nature variability is now the main issue to push this product on the market with robust properties. This research investigates the robustness of the poured earth binder. In this way, several clays (three montmorillonites, two kaolinites, and binary mixes at different proportions) were investigated. Their compacity (C) was determined following the water demand protocol with Vicat apparatus and compared to their consistency properties (liquidity and plasticity limits), and a correlation between these values is established. Different clay pastes prepared at different solid volume fractions were tested to define the influence of the clay nature on the paste consistency evolution. The results showed that clay nature for paste at high solid volume fraction does not influence constituency's evolution when their respectivecompacity is taking into account. It can be suggested that for a clay binder with a consistency close to C, which might be mandatory for poured earth application, only the swelling capacity might influence the mix design.

Abstract: For the multiscale damage behaviour simulation of advanced materials with hierarchical and random heterogeneous microstructures such as fibrous composites by finite element method, the mathematical homogenization method has been extended to the stochastic nonlinear multiscale method. A first-order perturbation based stochastic homogenization method was developed to calculate the microscopic strain, as well as the homogenized macroscopic properties considering randomness in the mechanical properties of constituent materials. Based on the calculated stochastic microscopic strain, the damage simulation framework was proposed for fibrous composites. For a demonstrated application, a numerical example of a single short fiber reinforced plastic composite was carried out. The damage propagation in the interphase between fiber and matrix was predicted in a stochastic way considering the physical random parameters for the interphase material model. The influences of the randomness on damage volume fraction and damage propagation of the interphase were discussed.

Abstract: Composite materials are created as a quite complex architecture which includes a fibre reinforcement structure and matrix material. Many material parameters play a role when composite structures are modelled, e.g. in finite element models. In addition to the properties of the raw fibre and matrix materials which are used, also geometrical parameters have a significant effect on structural characteristics. Fibre reinforcement geometry together with material properties of fibre and matrix determine homogenised material properties.The first part of the paper gives an overview of the most important processes which are used in composites processing industry. The factors which affect variability are also listed, and the effect of variability on material parameters is mentioned as well. The second part of the paper elaborates the identification of geometrical variability of the fibre reinforcement structure which is encountered with one particular type of composite material, namely a twill 2/2 carbon fibre weave with an epoxy matrix.

Abstract: Nebkha plays a major role in the ecological and environmental stabilization by accumulating wind-blown sediments around shrubs. Grain-size characteristics of different positions on nebkha reflect the sorting effect of aeolian dynamics. Based on the collected sand grains of different positions on four types of nebkhas at the southern fringe of Taklimakan Desert, China, this paper provided detailed insight into variability of the grain size of surface sand on nebkhas. The results showed that: a) Grain-size distributions on shield-shaped Karelinia caspica Nebkhas under natural condition had the larger spatial variability in comparison with the others. b) Grain size on nebkhas regularly showed the spatial variation. Grain size was increasingly larger along the windward slope upward, and then became finer along the leeward slope downward. c) The grain-size sortings of different positions on shield-shaped Alhagi sparsifolia Nebkhas under new reclaimed land were the best.

Abstract: A variability of energy consumption is the total variance divided by total mean consumption. Real data shows convergence of aggregated variability with the number of customers. We investigate the mathematical reasons of this phenomenon, as well as the subtleties of convergence rate. We show that the results for convergence on real data are consistent with the prediction of a simple sum of random correlated variables.

Abstract: Because the airport road surface is directly under the aircraft repeated taking off and landing, the airport road surface should have a good overall structure, high strength, good performance of anti overload fatigue. Under the long action of aircraft, road surface has been damaged. coupled with rising large wide body aircraft and air traffic, airport of old pavement disease gradually increased, the use of a sharp decline in performance, airport pavement performance directly affects the safty of the plane running. Through the research of the capital airport runway to central structure parameters, pavement on the basis of the findings, the distribution of the pavement structure parameters variability is analyzed, and the pavement damage condition of objective evaluation; combined with the drilling core sample laboratory test data and aviation business volume data, scientifically on the pavement damage character analysis, and provides a reference for future similar engineering treatment.

Abstract: Nutrients supplies play a crucial role in population distribution of food webs, and it is one of the most important challenges in both theoretical and applied ecology to better understand the ‘bottom-up’ effect. Here we analyzed a realistic food web containing one limiting nutrient and two producer-consumer interactions. Through the simulations of the mean population size and the variability of each species, we found that 1) in infertile environment the coexistence of species increases with nutrient supply; 2) the mean values of species abundance increase dramatically at then remain constant with the increase of nutrient supply; and 3) the stability of each population also increases and then remains constant. These results are inconsistent with the traditional predictions known as the ‘paradox of enrichment’, and our analysis may provide a solution to this paradox.